package Exercise;

import java.util.*;
import java.math.*;
public class Main{
    /**
     * 台阶题
     * @param args
     */
    public static void main(String []args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        BigInteger []array = new BigInteger[201];
        array[1] = BigInteger.valueOf(1);
        array[2] = BigInteger.valueOf(2);
        for(int i =3;i<=n;i++){
            array[i] = array[i-1].add(array[i-2]);
        }
        System.out.println(array[n]);
    }
}
